This invention relates to an improvement in an antiskid device for preventing wheels from falling into a skidding state when a brake is applied to a vehicle.
In such an antiskid device in general, braking pressure is caused to decrease when a sudden drop is detected in wheel velocity and then is allowed to increase upon restoration of the velocity of the rear wheels. Such braking pressure decreasing and increasing control in general has been accomplished with a power piston which is applied by a differential pressure between two air chambers. However, such a conventional method has the following drawbacks:
It is preferable to immediately effect reduction in braking pressure for preventing wheels from skidding and then to increase the braking pressure according to the status of restoration of wheel velocity. However, in the case of a conventional control method which has only one rate of increasing the braking pressure, such control cannot be accomplished according as whether or not an engine brake action which makes a great difference in the moment of inertia of a rotating body (hereinafter engine brake or no engine brake will be expressed as on or off actions of a clutch). Therefore, when the braking pressure increasing rate is arranged to be suitable for a clutch-on condition, the braking distance under a clutch-off condition becomes longer. Then, in cases where the braking pressure increasing rate is arranged to be suitable for a clutch-off condition, premature locking tends to take place under a clutch-on condition. On the other hand, in a conventional antiskid device where two rates of increasing the brake pressure are used as disclosed in U.S. Pat. No. 3,494,671, the brake pressure is controlled by use of the wheel acceleration so that the device is often erroneously operated by the noise signal contained in the wheel speed signal. The present invention is directed to the solution of such problems of the conventional antiskid devices.